Gemstones such as diamonds are classified according to weight and shape. The weight is commonly determined by measuring one to three dimensions of the diamond with a set of calipers and referring to appropriate tables for the corresponding weight. The measurements can be taken with a standard set of mechanical calipers which utilize either spring-loaded caliper jaws or thumbwheel control of the caliper jaws.
A digital measuring instrument which can be used for measuring diamonds is disclosed in U.S. Pat. No. 4,570,349 issued Feb. 18, 1986 to Finkelman et al. The disclosed instrument utilizes a set of caliper jaws movable by a thumbwheel. As the caliper jaws move, a rack and pinion arrangement sends signals to a computer. The computer stores tables for estimation of the gemstone weight which is displayed on a digital display. Digital calipers are also disclosed in U.S. Pat. No. 4,229,883 issued Oct. 28, 1980 to Kobashi and U.S. Pat. No. 4,612,656 issued Sept. 16, 1986 to Suzuki et al. The Kobashi patent discloses a transparent linear scale having calibrations and a light emitter positioned to direct light through the scale. A light detector on the opposite side of the scale counts the calibration lines as the caliper jaws move so as to determine linear travel. Kobashi also refers to another caliper device wherein a first rotatable member is rotated relative to a second rotatable member, and bright and dark patterns of the moire fringe are sensed to measure dimension. The Suzuki et al patent discloses a linear magnetic scale.
The prior art gemstone measurement devices have various drawbacks and disadvantages. Mechanical scales and prior electronically sensed linear scales provide limited resolution, since linear scales which move the same distance as the caliper jaws cannot be expanded. Devices utilizing thumbwheels for caliper adjustment are inconvenient and relatively slow in use. Spring-loaded calipers of the so-called "Leveridge" type snap back to the closed position and often dislodge gemstones from the calipers. The use of tables for determining gemstone weight based on dimensional measurement is relatively inaccurate and requires inconvenient interpolation between tabulated points.
It is a general object of the present invention to provide improved measurement methods and apparatus.
It is a further object of the present invention to provide improved methods and apparatus for measuring the dimensions and the weight of gemstones.
It is another object of the present invention to provide a handheld digital gemstone measurement apparatus having high accuracy.
It is a further object of the present invention to provide a handheld digital gemstone measurement apparatus having caliper jaws which are convenient to use.
It is still another object of the present invention to provide a handheld digital gemstone measurement apparatus which avoids the necessity for reference to weight tables and interpolation between tabulated values.
It is yet another object of the present invention to provide a handheld digital gemstone measurement apparatus which is self-contained and includes a direct readout of gemstione weight.
It is yet another object of the present invention to provide handheld digital gemstone measurement apparatus including a pneumatic device for controlling movement of caliper jaws.